'O God' in the Bible

We give thanks to God always for you all, making mention of you in our prayers;

For from you hath sounded forth the word of the Lord, not only in Macedonia and Achaia, but in every place your faith to God-ward is gone forth; so that we need not to speak anything.

For they themselves report concerning us what manner of entering in we had unto you; and how ye turned unto God from idols, to serve a living and true God,

For what thanksgiving can we render again unto God for you, for all the joy wherewith we joy for your sakes before our God;